The Effect of Stifle Angle on Stifle Kinematics following TPLO: An in vitro Experimental Analysis By Kelly Ann Johnson Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirement for the degree of Master of Science in Biomedical and Veterinary Sciences Approval Committee: Chair: Otto Lanz Ron McLaughlin Tisha Harper April 19, 2010 Blacksburg, VA Keywords: Tibial plateau leveling osteotomy, Kinematics, Cranial tibial translation, Internal rotation, Hyperextension Copyright 2010, Kelly A. Johnson The Effect of Stifle Angle on Stifle Kinematics following TPLO: An in vitro Experimental Analysis By Kelly Ann Johnson Objective: To determine the ability of the Tibial Plateau Leveling Osteotomy (TPLO) to restore normal joint kinematics in a cranial cruciate ligament (CrCL)-deficient stifle through a loaded range of motion. Methods: Paired pelvic limbs from 12 dogs were compared in an in vitro biomechanical study. Each limb was placed in a custom designed jig at 120° of stifle extension under an axial load of 20% body weight. Electromagnetic motion tracking sensors were placed on the distal femur and proximal tibia. A force was applied at approximately 10 N/sec to mimic the action of the quadriceps muscle. Force application allowed the limb to move from 120° to maximal extension. Positional data was acquired at 60 points/second. Each limb was tested under normal, CrCL-deficient, and TPLO-treated conditions. Results: The TPLO failed to normalize CTT within the CrCL-deficient stifle; however, values trended towards intact values throughout the range of motion. No significant differences were noted in internal rotation in any of the three conditions from 120° – 137°. Hyperextension values did not differ significantly between conditions. Conclusion: Data from this biomechanical model suggests that the TPLO fails to neutralize CTT throughout a loaded range of motion. Internal rotation and hyperextension values were not found to differ significantly between intact, CrCL-deficient and TPLO repaired stifles. The effectiveness of the TPLO in restoring normal biomechanics is more significant at greater angles of flexion. ACKNOWLEDGEMENTS Grant Information: The author would like to recognize the Virginia Veterinary Medical Association Grant for financial support. Additionally, Securos, Inc donated laboratory supplies to the project. Acknowledgements: The author would like to thank Pam Arnold for her help in acquisition, preparation and storage of the cadaver specimens, Dr. Steve Elder for his expertise and assistance with jig design, assembly and mechanical testing, and Dr. Stephen Werre for his help with statistical analysis. The author would additionally like to thank the graduate committee members listed above as well as Dr. Steven Arnoczky for their assistance in project design and document preparation. iii TABLE OF CONTENTS ABSTRACT………………………………………………………………... ii ACKNOWLEDGEMENTS………………………………………………... iii TABLE OF CONTENTS…………………………………………………... iv INTRODUCTION…………………………………………………………. 1 CHAPTER I: Literature Review…………………………………………… 3 A: Canine Stifle Anatomy………………………………………………. 3 B: Pathophysiology of Cranial Cruciate Disease……………………….. 8 C: Surgical Techniques………………………………………………….. 11 1. Intracapsular Techniques………………………………….. 12 2. ExtracapsularTechniques………………………………….. 15 3. Extracapsular Osteotomy Techniques…………………….. 18 D: Tibial Plateau Leveling Osteotomy…………………………………. 24 1. Surgical Technique………………………………………… 24 2. Biomechanics………………………………………………. 28 3. Complications……………………………………………… 31 E: Kinematics…………………………………………………………… 34 CHAPTER II: The Effect of Stifle Angle on Stifle Kinematics following TPLO: An in vitro Experimental Analysis…………………………………. 39 A: Objectives…………………………………………………………… 39 B: Materials and Methods……………………………………………… 39 1. Specimen Preparation……………………………………. 39 2. Biomechanical Testing Protocol…………………………. 40 3. Data Analysis…………………………………………….. 41 4. Statistical Analysis……………………………………….. 42 C: Results……………………………………………………………….. 43 1. Cranial Tibial Translation………………………………… 43 2. Internal Rotation………………………………………….. 44 3. Hyperextension…………………………………………… 44 D: Discussion…………………………………………………………… 44 1. Cranial Tibial Translation………………………………… 45 2. Internal Rotation………………………………………….. 49 3. Hyperextension…………………………………………… 51 4. Methodology……………………………………………… 52 5. Future Directions…………………………………………. 53 E: Conclusions………………………………………………………….. 54 REFERENCES…………………………………………………………….. 56 APPENDIX: Figures……………………………………………………….. 68 Figure 1: Custom Designed Loading Frame……………………………. 68 Figure 2: Cranial Tibial Translation……………………………………. 69 Figure 3: Internal Rotation……………………………………………… 70 iv INTRODUCTION The cranial cruciate ligament (CrCL) is known to prevent cranial tibial translation (CTT), limit excessive internal rotation, and prevent hyperextension of the stifle [1]. Deficiency of this ligament leads to three- dimensional kinematic changes in the stifle joint throughout the entire gait cycle [2]. With an intact CrCL, motion during the swing phase occurs in three planes while in the stance phase motion is limited to flexion and extension. Rupture of this ligament alters stifle motion such that motion in three planes is present during both the swing and stance phases. Additionally there is significant CTT that occurs throughout the stance phase [2,3]. These changes in gait kinematics are thought to alter the load distribution across the articular surfaces of the femur and tibia promoting the development of osteoarthritis [4,5]. The ideal surgical technique to address a CrCL-deficient stifle should restore all three functions to the stifle throughout the entire gait cycle and prevent the progression of osteoarthritis. The complex and dynamic functions of the CrCL has made the development of a consistently effective surgical technique challenging which is evident by the vast array of proposed surgical techniques as well as the failure of a single technique to prove superior in the reestablishment of normal limb function [6,7] or prevention of the progression of osteoarthritis [8]. The tibial plateau leveling osteotomy (TPLO) is a commonly performed technique for repair of a CrCL-deficient stifle. The TPLO is based on the theory that the caudal slope of the tibial plateau promotes cranial translation of the tibia during weight bearing. The TPLO neutralizes this slope resulting in pure compression without CTT during loading [9]. The ability of the TPLO to eliminate this CTT at a standing angle has been demonstrated in three separate biomechanical cadaveric studies [10-12]. While these studies validate the principle function of the TPLO, only one study accurately addresses the effect of the TPLO on limiting excessive internal rotation [12]. In that study, CTT and internal rotation were evaluated in intact, CrCL- deficient and TPLO repaired stifles. While marked CTT and internal rotation were noted in the CrCL-deficient stifle, no significant differences were noted 1 between intact stifles and TPLO repaired stifles, suggesting the TPLO restores two of the three functions of the CrCL at a standing angle. While these biomechanical TPLO studies validate the normalization of the relationship of the femur and tibia at a standing angle, the vital assessment of the three-dimensional changes throughout weight bearing has not been performed. Two in vivo experimental studies have described the three-dimensional kinematic changes that occur in the absence of the CrCL [2,3]. While both studies documented the presence of CTT, changes in rotation were conflicting. Additionally a single in vitro biomechanical study that evaluated the three-dimensional changes throughout a range of motion in an intact and CrCL-deficient stifle found that from 30° to 95° of flexion there were no significant differences in CTT or internal rotation between the two conditions [13]. However, the limbs were not loaded to mimic weight-bearing, making comparisons to other studies at loaded angles difficult. While each of these studies evaluates a range of motion, none assess the effect of the TPLO. To the authors’ knowledge no study has concurrently evaluated the effect of the TPLO on CTT, internal rotation and hyperextension through a loaded range of motion. 2 CHAPTER I: Literature Review A: Canine Stifle Anatomy The canine stifle joint is a complex, synovial joint that allows motion in three planes. While the primary movement of the stifle joint is flexion-extension the anatomy of the joint also allows for cranial-caudal translation, internal-external rotation, varus-valgus angulation, medial-lateral translation and compression-distraction [2]. It is composed of 3 long bones: distal femur, proximal tibia, proximal fibula; 4 sesamoid bones: popliteal, medial fabella, lateral fabella, patella; 2 menisci; 4 major ligaments: medial collateral, lateral collateral, cranial cruciate (CrCL), caudal cruciate; a joint capsule; and multiple muscles [14]. Each of these components works in concert to contribute to the dynamic stability of the stifle joint. The distal femur has two major articulations formed from three articular surfaces. The femoropatellar articulation is formed by the cranially positioned trochlear groove and the patellar sesamoid. This articulation dynamically lengthens the lever arm of quadriceps muscle during motion improving the efficiency of extensor function [15]. The femorotibial articulation is formed by distinct lateral and medial condylar articulations with the tibia. This is the major weight